When user equipment (referred to as UE) is handed over, after the UE is handed over to an E-UTRAN Node B (referred to as eNB) on the destination side, the UE needs to be configured by using a new security algorithm. However, with regard to the scenario of handover failure of the UE, the UE may initiate a re-establishment request, and uses the old security algorithm (i.e. a security algorithm used by an NB on the source side) instead of the security algorithm. Therefore, it is mentioned in the prior art that, when a UE handover is performed, an eNB on the source side needs to transmit a security algorithm thereof to an eNB on the destination side, wherein the security algorithm is used for application in the scenario of re-establishing a radio link.
However, in the prior art, it is only mentioned that the security algorithm of the eNB on the source side is transmitted to the eNB on the destination side and the security algorithm is applied to a potential scenario of re-establishing the radio link, but it does not distinguish the specific scenario of re-establishing the radio link. However, there are multiple scenarios of re-establishing the radio link, and some of the scenarios of re-establishing the radio link are not as a result of the handover failure of the UE. If the security algorithm of the UE falls back to the old security algorithm under this scenario, the problem of fallback process failure may happen.
For example, in the scenario of a non-contention based handover, UE receives Msg 2 (the second message randomly accessed), and at the moment, the UE considers that it is handed over successfully. However, because of the quality problem of a radio link, when a Reconfiguration Complete message is sent to an eNB on the destination side, the maximum number of re-transmission is exceeded in a radio link control (referred to as RLC) layer on the UE user plane, and at the moment, the UE may also initiate a re-establishment request to the eNB on the destination side. According to the prior art, since the eNB on the destination side does not receive the reconfiguration complete message, the eNB on the destination side considers that the handover is unsuccessful, and may update a security algorithm of the UE to the old security algorithm if receiving the re-establishment request at the moment. However, since the UE considers that it is handed over successfully at the moment, the security algorithm used by the UE has already been a new security algorithm. However, because of the failure to send the reconfiguration complete message to the eNB on the destination side, the UE sends the re-establishment request to the eNB on the destination side and it is not handover failure of the UE in real sense, and thus a security algorithm fallback process performed by the eNB on the destination side must fail.
In the traditional art, a security algorithm fallback process is performed inaccurately in a procedure of re-establishing a radio link, thus rendering the problems of the failure of re-establishing the radio link and the lower success rate of re-establishing the radio link.